1. Field of the Invention
The present invention relates to devices for the formation of granulated or agglomerated substances, in general, and to a device in which solid substances and liquids can be mixed and dried in the same container during formation of the granulated or agglomerated substances, in particular.
2. Description of the Prior Art
Fluidized bed driers which have a container for holding the substance to be dried are known from Swiss Pat. No. 444,046 as well as from the corresponding U.S. Pat. No. 3,394,468 and from Swiss Pat. No. 475,786. The bottom of the container is provided with openings. The space above the container contains a filter and is connected with a suction fan. During operation, warm air is supplied to the area under the bottom of the container. The warm air, with the help of the suction fan, is drawn through the container and the granular substance contained therein. In doing so, the substance to be treated is whirled about.
For the granulation process, liquid is sprayed into the whirling space through at least one spray nozzle arranged at the top of the container. In this way, the liquid is mixed with the whirled-about granular substance and a granulated or agglomerated substance is formed. In order to dry the substance, warm air continues to be drawn through the granulated or agglomerated substance for a certain period of time after the termination of the spraying process. When the suction fan is cut out, the granulated substance settles in the container. The container, after being pushed out of the structure of the device, is emptied and charged with a new substance to be treated.
The granular material to be treated consists frequently of a mixture of different solid substances. The granules consisting of different solid substances have, in general, different densities and are possibly also of different sizes. The result is that a certain fractioning takes place during the whirling process. The granulated substance formed with the spraying of the whirled-about granules becomes nonhomogeneous which represents a considerable disadvantage.
Granulating devices and a device for the coating of solid substance particles are known from German Interpretation Publication Nos. 23 41 504 and 19 37 424, as well as German Disclosure Publication Nos. 26 43 121, 25 51 578 and 24 18 552. The devices disclosed in these documents are similarly designed as fluidized bed driers, as described above, and some of these devices additionally include a rotary stirrer or chopper arranged in the container. Also, the material to be treated by these known devices is whirled about and sprayed with a liquid in the whirling space. Thus, all of the prior art devices just described have the disadvantage that a certain fractioning and disintegration takes place during the whirling-about and spraying of a mixture.
This disadvantage has been eliminated to a certain extent by first mixing the solid substances in a mixer in a dry condition. This dry mixture is then sifted on a screen and transferred into a mixing-kneading device which is also supplied with the liquid required for the granulation process. Subsequently, the powdery mixture and the liquid are stirred with stirrers and kneaded in the mixing-kneading device. The humid substance formed in this way is then transferred into a granulating press in which the humid substance is pressed through a screen plate. The rod-shaped material formed in this manner is then charged into the mixing container of a fluidized bed drier and dried there with warm air until the material is more or less crumbled. When the material is dried and crumbled, it is taken out of the drier and transported into a separate screening device where it again goes through a screening process. The granulated material thus formed can then be introduced, for example, into a preforming press for formation into tablets.
The process just described actually produces granulated material with a homogeneous composition but has the disadvantage that, when pressed through the screen plate of the granulating press, particles are formed with a regular cylindrical shape and with firm cylindrical surfaces which make subsequent tablet formation more difficult. Another disadvantage is that a comparatively large number of separate devices are required to form the granulated material, and the intermediate product must be taken manually from one device to the next by work personnel.
A granulating device is also known from German Disclosure Publication No. 25 38 267 in which components, used in the formation of granulated material, are first mixed in dry condition in a container and subsequently granulated in the same container by adding a liquid, mixing continuously, and finally drying with a flow of air. A mixing tool which can be rotated around a vertical axis is available in the container for the mixing operation. The air, serving drying purposes, can be introduced into the container through a socket penetrating into the upper area of the container as well as through the shaft of the mixing tool. However, this kind of air supply results only in a relatively slight and irregular whirling-about of the mixed material and, thus, in a correspondingly low drying effect. Since the mixed material is to whirled upward, the air introduced from above has a comparatively low effect. Furthermore, because the air is supplied from below through the shaft of the mixing tool into the container, it has a whirling effect only across a small area of the container bottom. Additionally, only a comparatively small amount of air per unit time can be introduced through the shaft.